Heat oven to 180C/160C fan/gas 4. Line a 23cm cake tin with a square of baking parchment so the corners stick up (this will help you to lift the rolls out).
Unroll the croissant dough from the can and lay it out on your work surface. Cut it into three sections along the dotted lines, but don’t cut the diagonal line. Spread over a quarter of the butter.
Mix the cinnamon and sugar together. Using one square of dough at a time, sprinkle over 2-3 tsp of the sugar and roll up the dough. When you have three rolls, cut each one in half and then each half into three. Arrange the rolls in the tin in two circles – you need to spread them well apart as they will rise and spread. Stick the end bits in among fatter pieces from the centre of the rolls so they cook evenly. Bake for 15 mins or until the rolls are risen and cooked through.
Meanwhile, heat the remaining sugar mix with the remaining butter until you have a thick caramel (don’t worry if some of the butter separates out, it will soak into the dough). When the rolls are cooked, pour over the caramel. Leave to cool a little, then eat warm.